A wide range of medical treatments have been previously developed using “endoluminal prostheses,” which terms are herein intended to mean medical devices which are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries such as those located within coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted luminal wall.
A number of vascular devices have been developed for replacing, supplementing or excluding portions of blood vessels. These vascular grafts may include but are not limited to endoluminal vascular prostheses and stent grafts, for example, aneurysm exclusion devices such as abdominal aortic aneurysm (“AAA”) devices that are used to exclude aneurysms and provide a prosthetic lumen for the flow of blood. Typically these endoluminal prostheses or stent grafts are constructed of graft materials such as woven polymer materials (e.g., Dacron,) or polytetrafluoroethylene (“PTFE”) and a support structure. The stent-grafts typically have graft material such as a woven polymer, secured onto the inner diameter or outer diameter of a support structure that supports the graft material and/or holds it in place against a luminal wall.
One very significant use for endoluminal or vascular prostheses is in treating aneurysms. Vascular aneurysms are the result of abnormal dilation of a blood vessel, usually resulting from disease or a genetic predisposition, which can weaken the arterial wall and allow it to expand. While aneurysms can occur in any blood vessel, most occur in the aorta and peripheral arteries, with the majority of aneurysms occurring in the abdominal aorta. Typically an abdominal aneurysm will begin below the renal arteries and may extend into one or both of the iliac arteries.
Aneurysms, especially abdominal aortic aneurysms, have been treated in open surgery procedures where the diseased vessel segment is bypassed and repaired with an artificial vascular graft. While considered to be an effective surgical technique in view of the alternative of a fatal ruptured abdominal aortic aneurysm, the open surgical technique suffers from a number of disadvantages. The surgical procedure is complex and requires long hospital stays due to serious complications and long recovery times and has high mortality rates. In order to reduce the mortality rates, complications and duration of hospital stays, less invasive devices and techniques have been developed. The improved devices include tubular prostheses that provide a lumen or lumens for blood flow while excluding blood flow to the aneurysm site. They are introduced into the blood vessel using a catheter in a less or minimally invasive technique. Although frequently referred to as stent-grafts, these devices differ from covered stents in that they are not used to mechanically prop open natural blood vessels. Rather, they are used to secure an artificial lumen in a sealing engagement with the vessel wall without further opening the natural blood vessel that is already abnormally dilated.
Most currently used AAA devices comprise a main body portion fixed at the infrarenal aorta junction. The prostheses are typically secured to a vessel wall above and below the aneurysm site with at least one attached expandable annular spring member that provides sufficient radial force so that the prosthesis engages the inner lumen wall of the body lumen to seal the prosthetic lumen from the aneurysm. The devices are typically delivered by initially placing a main body endoluminally and engaging the device to the aorta wall by a series of self-expanding annular spring members. The main body is frequently a bifurcated device with a long and short iliac leg for directing blood flow through the iliac arteries. A contralateral leg is delivered and coupled to the short leg of the bifurcated main body graft. Iliac and/or aortic cuffs then may be delivered if desired to improve or extend deployment or fixation through desired regions.
In general, in many diseased vessels, the area for prosthesis fixation above an aneurysm or other diseased portion may be limited, making secure fixation of the prosthesis more difficult. In addition, over time there is a possibility that the prosthesis may migrate. A number of devices or solutions have been proposed to improve fixation. Super renal fixation has been provided to improve fixation. However, particularly in a diseased patient, there may be suprarenal cholesterol or atheroma plagues that may dislodge, fragment or release from the supra renal area. In other devices, other mechanisms have also been used to engage the vessel walls such as, for example, hook like members that puncture the vessel wall. The hooks traumatize the tissue and therefore may be undesirable. Increased radial force has been proposed to improve fixation as well. However, in some patients, migration may occur when the neck or region in which the graft is deployed expands or otherwise changes over time and thus increased radial force may not prevent migration in such a situation.
It would accordingly be desirable to provide a stent graft fixation system that provides improved fixation with a confined or limited area upstream of an aneurysm site. It would also be desirable to provide a device that reduces migration of the stent graft. It would also be desirable to provide an improved fixation system for an endoluminal prosthesis that reduces trauma to tissue.